1. Technical Field
The present invention relates generally to a method of realizing digital broadcasting service and, more particularly to an apparatus and method of interfacing a set-top box and a point of deployment (POD) for pay-per-view service, in which the pay-per-view service is provided while observing an OpenCable standard in realization of bi-directional digital cable broadcasting.
2. Related Art
Digital broadcasting may be classified into digital terrestrial broadcasting, digital satellite broadcasting and cable broadcasting according to the transmission medium. Currently, digital satellite broadcasting is activated all over the world, and digital terrestrial broadcasting is in progress in some countries, such as the United States of America and Europe.
Digital broadcasting compresses information of channel-specific programs on the basis of an MPEG (Moving Picture Experts Group) coding standard or the like with high efficiency, and multiplexes and transmits the programs corresponding to the plurality of channels on the basis of transmission medium-specific digital modulation modes. Thus, digital broadcasting can broadcast tens to hundreds of channels without using numerous repeaters as in analog broadcasting.
In general, a broadcasting system for processing the cable digital broadcasting includes a head end which transmits broadcasting related digital signals and receives and processes data uploaded from subscribers, and a set-top box which receives digital signals transmitted from the head end, converts the received digital signals into analog signals, and reproduces the converted analog signals into original audio and video signals.
The head end refers to a main control center equipped with technical equipment which receives, produces and retransmits the programs from a satellite or other location through a system network in a cable television (TV) system. The set-top box is generally a home communication terminal required to use multimedia communication service inclusive of video-on-demand service.
With this broadcasting system, each cable system operator (SO) produces programs, content, and other data of cable TVs, or is supplied with them from producers, and transmits them to the subscribers. Then, each subscriber looks at the programs or other data transmitted from the cable SOs so as to watch the broadcasting which he/she wants to watch.
With respect to video and audio compression technology in the cable digital broadcasting, MPEG-2 is adopted all over the world as a standard. Its modulation mode is a QAM (Quadrature Amplitude Modulation) mode, which is one of the digital modulation modes which varies amplitude and phase according to a digital data signal to be transmitted, and which is more suitable for transmission of high-efficient data within a limited transmission band. In particular, 64 QAM digital frequency modulation technology is mainly used to transmit downstream data transmission in a coaxial cable network, and supports a transfer rate of up to a maximum of 28 Mbps on a single 6 MHZ channel.
Most technology used for cable broadcasting is used in the digital TV, and has a difference in that the digital TV technology makes use of the transmission medium called wireless, while the cable TV broadcasting makes use of the transmission medium called wire. Therefore, cable broadcasting has an advantage in that it is still excellent in providing bi-directional service compared with terrestrial broadcasting.
The set-top box (digital broadcasting receiver) in digital broadcasting is mainly directed to decoding digitized broadcasting and managing information transmitted by the head end which is installed at a local cable TV company for the cable TV or cable modem service which is provided to the subscribers, and transmitting analog signals to the TV. The set-top box receives broadcasting and managing information from the head end, such as an audio/video server, a service information server transmitting broadcasting channel information, and a conditional access server.
In this digital cable broadcasting, bi-directional service has recently made an appearance. The concept of “bi-directional” means that, when the desires of a user are transmitted to the multimedia, the information desired by the user is provided. New media may be media intended to technologically reproduce a bidirectional function which has been lost. This means that the user has a bi-directional function and a network application function. Accordingly, this means that the user can edit and process a variety of data that he/she has.
A field in which the bi-directional system is best applied commercially is the operation of pay-per-view. Up to now, the subscriber applies a specific program to the cable system. However, in a new bi-directional converter system, it is possible to select the program by simply pushing a button on a remote controller. A computer at the head end automatically and immediately processes, controls and manages this program application of the subscriber.
In order for the pay-per-view system to be applied to digital cable broadcasting, it is necessary to adjust watching authorization according to the subscriber. It is a so-called CA (conditional access) system that takes charge of this role. The CA system performs a combination of scrambling and encryption functions, wherein scrambling serves to prevent any unauthorized person from seeing a signal, is transmitted together with any scrambled signal, and then is used together with a secret key that serve to descramble the scrambled signal. It is encryption that serves to protect the secret key at this time.
The CA system may be built into the set-top box, but it is located at a POD (Point of Deployment) that is a separate device independent of the set-top box.
The POD is a conditional access card (so-called cable TV card) that contains information on the subscribers of cable TV so as to permit paid broadcasting of the cable TV to be watched only when being identified as the subscriber. The POD is composed of a PCMCIA card together with a smart card containing the subscriber information, and it is issued to the subscriber by a cable TV broadcaster, and is inserted into and used in the set-top box. The POD permits only qualified or authorized pay subscribers to decode the encrypted signal so as to watch cable TV. In addition, the POD makes it possible to perform the function of billing of pay service by transmitting billing and subscriber managing information to the head end of the cable SO. This mode, wherein the cable TV card is separated from the set-top box, is called “OpenCable.”
A key element of the OpenCable service is mandatory use of the POD. In other words, the POD is a device having a conditional access system (CAS) and copy protection taking a type of the smart card enabling the cable TV service provider to identify the subscriber and use type, and is premised on a type being separated from the set-top box.
The set-top box for existing pay-per-view service, as described above, is not applied to the OpenCable standard because it has the built-in CA system. In addition, specific protocols related to the set-top box for the pay-per-view service are different according to a CA system manufacturer, or are not opened due to security, and thus are not standardized.
This problem gives rise to a result that interfacing protocols between the set-top box for the pay-per-view service and the POD are not harmonized under the OpenCable standard adopted as the internal digital broadcasting. Thus, any need to solve this problem is raised.